The present invention relates to a ball bushing for linear motions, comprising a number of closed loops for rolling bodies between an outer sleeve and a shaft or the like, the rolling bodies being loaded in at least one part of the loop.
In such a ball bushing the rolling bodies are loaded between the outer sleeve and the shaft, and thereby it is common practice to provide the loaded parts of the shaft and/or the sleeve with special raceways of a wear-resistent material. Further, the bushing is generally provided with a cage element situated between the shaft and the sleeve, which element is provided with closed ball paths for guiding the balls. As an example of such a bushing, reference can be made to the Swedish patent publication, No. 361,342. In this publication, a ball bushing is described comprising a closed outer sleeve and a cage element adapted inside it, the cage element comprising a number of closed ball paths and surrounding a shaft. The loaded balls are not contacting the sleeve directly, but roll against a metal bar, which is supported by the inner surface of the sleeve. The metal bar is kept in position by parts of the cage element. The outer sleeve is designed so that a certain deformation of it is possible by changing the bore diameter in a housing surrounding the sleeve. Thereby it is possible to pre-stress the bushing as desired, and, moreover, the pre-stressing can be adjusted.
A bushing of the type described above has, however, certain drawbacks. For example, the shape of the outer sleeve is rather complicated, which makes the production cost high. Tests have been carried out to produce it by extrusion. Aluminum has been used, because this material requires comparatively low press forces, which makes the tools cheap, and because the pre-stressing of the completed bushing is easy to carry out. However, it has been shown, that also this method is expensive, and furthermore, by the motion of the balls, a quick wear of those parts of the sleeve which define the unloaded parts of the ball paths takes place. It is also known to design the outer sleeve as a unit in a polymer material, see for example, the German Offenlegungsschrift No. 2,402,401. The loaded parts of the sleeve are hereby made of metal bars, which are mounted by being pressed radially inwards in axially extending slots in the sleeve. Also, such sleeves have a comparatively complicated shape, because they, in principle, consist of a hollow cylinder with a very special shape of the bore, in which axially extending slots are provided. The rims of the slots have thereby a special shape in order to make it possible to fit the metal bars. The production of such sleeves is therefore complicated.